In previous lessons, we've explored the fundamentals of Test Driven Development (TDD), the Red-Green-Refactor cycle, and the setup of a testing environment using C++, Google Test, and Google Mock. Now, we shift our focus to a key aspect of TDD: managing dependencies. Managing dependencies ensures that each unit of your application can be tested in isolation, which is crucial in TDD for maintaining code reliability and robustness.

In this lesson, we will examine how to use abstract classes and pure virtual functions in C++ to manage dependencies effectively. Using simple examples, we will demonstrate how to apply the Red-Green-Refactor cycle in this context. We'll use C++ with Google Test and Google Mock to provide practical context. Let's dive in.

Dependencies in software development refer to the components or systems that a piece of code relies on to function properly. In the context of testing, dependencies can complicate unit tests because they might introduce external factors that affect the test outcomes. To ensure tests are isolated and independent, we use abstractions.

An abstract class in C++ acts as a base class that defines the interface for derived classes using pure virtual functions. By programming against abstract classes, you can easily swap out implementations, making code more modular and test-friendly.

For example, consider a logger that a component uses to record actions. By abstracting the logger as an abstract class, you decouple the component from a specific logging implementation. This abstraction allows you to replace the actual logger with a mock or fake when testing, thus focusing on testing the component, not its dependencies.

We'll create a simple logger abstract class called ILogger to demonstrate dependency management. This abstract class will define a pure virtual method , which our will use: